1. Field of the Invention
This invention relates to current sensors.
2. Discussion of the Background
Due to the need for miniature inductor structures for use in micro-modules, such as those used in the hearing aid industry, there have been developed not only more sensitive and efficient devices but those that are more economical. This need has resulted in more precise and concentrated material refinement with the associated development technology. In the search for a tiny, reliable, sensitive telephone coil, the current sensor of the present invention was produced.
It is well known that a wound toroid coil provides a good current transformer. If a wire carrying a current to be measured is passed through the hole in the toroid a one-turn primary winding is formed and the turns ratio from the primary to the secondary is determined by the number of turns on the toroid core. Based on electrical characteristics, the theoretical ideal form for inductance devices is a toroid. However, toroid coils and transformers are difficult and expensive to construct, particularly because of the difficulty in applying multiple windings to completely closed toroid cores in mass production.
In an attempt to solve this problem U.S. Pat. No. 3,238,484 provides a method of making an inductance device by applying a coil structure to an arched magnetic core member of substantially uniform cross sectional area and having two ends, by applying a magnetic bridge member directly across the ends of the arched member, by then adjusting the spacing between the bridge member and the arched member until the winding exhibits a predetermined value of inductance, and by finally fixing the relative position of arched and bridge members, thus making the adjusted D-shaped core juncture permanent.
In contrast, the present invention provides a straight magnetic core which allows for ease in winding a multi-turn coil with a large number of turns in a simple winding chuck while protecting the coil against stress and strain in retaining the core straight under the coil by bending the ends of the straight core beyond the coil into a curved portion until the ends make magnetic contact and are permanently connected as by welding, crimped or wire wrapped to provide a single connection. Dacy on the other hand provides multiple connection between multiple sections of curved core portions.
Another pertinent patent is U.S. Pat. No. 1,735,092 which is directed to a transformer having effectively a single-turn core that is provided with a plurality of loops therein for the purpose of increasing the sensitivity, which teaches away from the use of a single-turn device. Other patents of interest are: U.S. Pat. No. 2,137,878; U.S. Pat. No. 2,659,845, U.S. Pat. No. 2,958,835; and U.S. Pat. No. 1,808,670.
Toroid core transformers are used extensively in electronics for power conversion and for signal transfer even at high frequencies. They serve a purpose which other devices cannot fill. However, the toroid transformer suffers from being expensive to produce particularly where a large number of turns are required.